Both Hartge and Schnitzer built a couple of these cars as well in the early nineties.
There was actually a discussion about these cars on the E34 discussion last month, the conclusion was that, opposite to my initial thoughts, the car's balance wasn't too badly affected due to the minimal weight difference between the V12 and the standard inline six.
*Now here's a thought*
If you could find a totaled McLaren F1, this E34 car would be ideal as a basis for the ultimate sleeper...